An arrangement for extracorporeal circulation of blood generally comprises a bloodline and several components for circulation of the blood such as a dialyzer and a drip chamber. In the extracorporeal circuit it is important to avoid stagnation of blood in order to avoid clotting. Clotting may in severe cases lead to dire consequences for the patient.
Extracorporeal circuits of the above kind are for example used in different kinds of medical treatment such as hemodialysis, hemodiafiltration, hemofiltration, plasmapheresis, plasmafiltration, liver dialyis, immunotherapy, irradiation and phototherapy. These extracorporeal circuits have a common feature in that they draw blood from a patient, circulate the blood through a treatment unit and then return the treated blood to the patient. This circulation outside the patients body for treatment begins and ends with the passage of the blood through a single or dual lumen catheter or needle system, generally assisted by a pump to provide a regulated flow of blood throughout the treatment. Such systems most typically use one or more roller pumps to set a specified rate which is carefully monitored and controlled.
In general it is preferable that the entire blood passage through the extracorporeal circuit from a withdrawal needle to the return needle have substantially the same diameter with the possible exception of a dialyzer component so that blood flow velocity is substantially uniform and constant through the circuit. A benefit of an extracorporeal circuit having a uniform inner diameter and substantially continuous flow passages is that the blood tends to flow uniformly through the circuit and does not form stagnant pools within the circuit where clotting may occur.
It has been found that the placement of the bloodline with respect to the inlet to a component for circulation of the blood, e.g. a dialyzer or a drip chamber, influences the distribution of the blood flow in the component. In cases where the bloodline is placed in such a way that the flow of blood is not well distributed so called dead zones may develop where the blood may stagnate and clot. Due to the fact that the bloodline is flexible and loosely dressed on for example a dialysis monitor it is cumbersome to place it in a way that secures a defined distribution of the blood in the component for circulation of the blood.